Nope, doesn't work that way. "Edit" keeps the post in place, "Reply" puts you at the end of the line.
A lot of Group Build threads set up an initial post for the announcement, a second post to list participants and their builds as they sign on, and a third to post pictures of completed models.
Those second and third posts get updated a lot. They work best if they stay where they are.
Another thing that'll freeze your post is if it gets quoted in a reply.
When faced with your situation, I've concluded that it's easiest to just put up a new post and call it "the pictures that photobucket stole from me".